a) Field of the Invention
The present invention generally relates to decorative papers and impregnated papers for manufacturing decorative boards which are formed by thermal pressing.
b) Description of the Related Art
To manufacture a piece of melamine decorative board, a piece of raw paper with good permeability is colored or printed with patterns, and by impregnating thermosetting resin into the resultant decorative paper, a piece of impregnated paper is obtained. A laminated material is made by placing the piece of impregnated paper on a piece of impregnated kraft paper (kraft paper impregnated with thermosetting resin) and formed by thermal pressing. Finally the laminated material is bonded onto a surface of a base material with an adhesive. The product is known as high pressure melamine decorative board.
Although high quality products can be obtained from this manufacturing process, there are disadvantages. It requires a continuous pressing over a long period of time, i.e., cold pressing, hot pressing and further cold pressing, to laminate the impregnated paper and the impregnated kraft paper. Further, sanding of the adhesive surface is required, and numerous processes are involved. Because of this, in recent years a process has been employed in which an unhardened impregnated decorative paper is directly put together with the base material, and at the same time formed without layering it with the impregnated kraft paper. An example of this is so-called "short cycle" melamine decorative board, and a special fast hardening melamine resin is used. However, it is easy to compromise the characteristics of the surface such as a decrease in luster in the process where water content starts evaporating as steam and escapes from the formed surface. The water is contained in a wooden base material or a piece of impregnated paper, or created by condensation reaction of the thermosetting resin. This occurs because the impregnated resin must be hardened in a short time, and the pressing of the impregnated paper and the base material is done at a quite high temperature. The product is also taken out of the press at a high temperature.
Since this problem is more accentuated where a mirror plate used for pressing which comes in contact with the impregnated paper surface in the press process exhibits high luster, it is common to use a mirror plate whose reflectivity is less than 50% on the surface in manufacturing short cycle melamine decorative boards. Otherwise it is difficult to control the luster and its consistency.
Further, in this manufacturing process, since the thermosetting resin on the reverse side of the impregnated paper or the thermosetting resin absorbed in the impregnated paper is a bonding agent for the wooden base material, a portion of the impregnated resin shifts to the side of the base material during the forming process. At the same time, a portion of the resin on the impregnated paper surface is absorbed, and the amount of hardened resin which is left on the surface at the end of the processes decreases. As a result, abrasion resistance of the decorative paper layer of the product tends to be insufficient. Since the shifting amount of the impregnated resin depends on the properties of the base material surface or those of the impregnated raw paper, the surface physical properties can vary widely.
In order to solve problems stated above in the manufacturing of short cycle melamine decorative boards, the amount of volatile component included in the base material or the impregnated paper is decreased as much as possible (and controlled to about 6%). The amount of thermosetting resin included in the impregnated paper is somewhat increased, and at the same time, the amount of catalyzer within the impregnated resin is also increased. However, the effect is not sufficient, and especially in the latter, heat stability decreases in the forming process and the properties of the surface of the product tend to be poor.
It is an object of the present invention to solve the above-stated problems in decorative board manufacturing in which a sheet of impregnated paper is directly bonded with a base material. The present invention relates to a provision of a decorative board having an excellent abrasion resistance, luster and consistency in the physical properties of the surface.